Electric-powered lighting in commercial buildings in the United States accounts for 23% of the electricity consumed. Although the efficacy of the fluorescent lamp, the dominant electric-powered lighting source in the commercial sector, is unlikely to increase significantly during the next decade, there are significant opportunities to reduce energy consumption used for lighting in commercial applications. These opportunities are created by using daylight (or solar light) more effectively by controlling the amount of electric-powered light delivered in response to available daylight. Studies undertaken over the past 20 years have consistently shown that electric energy used to generate light in commercial buildings can be reduced by 10%–30% by using a photosensor to switch electric-powered light when daylight is available, and to maintain the electric light levels at design levels throughout lamp life. Consumers perceive daylight dimming systems as ineffective, however, and are reluctant to install lighting control systems that dim or switch electrical lighting fixtures when daylight is present.
Illumination control is difficult because the sensor, for practical reasons, is usually located on the ceiling or high on a wall, while “useful” illumination is more closely associated with illumination of the task or work-plane (typically a desktop). Moreover, the ratio for the illumination level at the task location to the illumination level at the operational sensor location is different for daylight and electric light. This difference is due to multiple factors including room geometry and incident angles of the light source to the work surface.
A lighting control system employing a control algorithm that merely tries to maintain a constant sensor signal will not provide, in fact, adequate useful illumination as the distribution of light within the space changes to a higher composition of daylight. Task-to-ceiling illumination ratios typically vary by a factor of five or more when going from the conditions of 100% electric-powered lighting to 100% day light. Therefore, the sensor signal does not increase proportionally with the illumination of the task location. The typical outcome is that too many electric-powered lights are switched off in the presence of daylight. Occupants then complain of insufficient light and the control is disabled.
To overcome the problem of variable task-to-sensor light level ratios for daylight and electric light, proportional control systems have been suggested. Proportional control systems require commissioning, however, which can be difficult and expensive thus limiting their effective use. Most products on the market do not offer sufficient adjustment capabilities (both in terms of adjustment mechanics and range of adjustment) to allow easy commissioning. Many photosensors must be moved to different locations using a trial-and-error approach to get satisfactory performance. Such movement is time consuming, aggravating, and expensive. For at least these reasons, commissioning is often not done completely or properly and the systems fail to work as intended.
The cost of installation and commissioning is another reason that consumers are reluctant to install lighting control systems to switch electrical lighting fixtures when daylight is present. Commissioning current photosensor lighting control systems typically requires the use of extraneous light meters. Frequently commissioning must be performed during multiple daylight conditions, sometimes including measurements in the absence of daylight.
Another problem is that some users do not prefer the same level of illumination as the proportion of daylight to total available light changes. Preference studies have shown that, under some circumstances, people want higher levels of illumination as interior daylight levels increase.
An additional photosensor problem is that, when different sensors are used for commissioning measurements taken at different locations, they can have different sensitivity to infrared (IR) radiation. This difference affects system performance because daylight contains much more infrared radiation than fluorescent lighting for the same amount of visible light. Therefore, the photosensor switches the electric lighting when it is essentially sensing invisible IR radiation rather than visible light.
Photosensors have been available for use in interior spaces for many years, but during this time have achieved dismal market penetration due to a number of factors. One primary reason for their lack of market acceptance has been cost. Current photosensors can range from a low of nearly $50.00 to over $100.00 each. A building owner must then factor in the cost of installation. Because nearly all existing photosensors require additional wiring, the cost to install them in existing buildings becomes prohibitive. Even in new construction, this need for additional wiring can add to installation costs. After installation, each photosenor in a building must be individually commissioned. This is a difficult and time-consuming process, often requiring several return visits by a lighting specialist before building occupants are satisfied with the results.
Most current photosensors are also designed to work in conjunction with dimming electronic ballasts in fluorescent lighting systems. These ballasts typically cost three times as much as conventional “instant-start” ballasts and in some cases may actually shorten the life of the fluorescent lamps they operate. In addition, because dimming ballasts are designed with “rapid-start” circuitry (to maintain the lamp cathode heating necessary for dimming) they use more energy than instant start ballasts, even when the lamps they operate are not being dimmed. Many dimming ballasts are also designed to maintain the light output of the lamps they operate about at least 5% when used with photosensors. Consequently, the lamps are always on. This uses some amount of energy (about 15%) as opposed to a 100% savings when there is a complete shut off. Finally, after incurring all of these additional costs, a building owner is never assured that the photosensors installed in his or her building will operate effectively over time. Because each photosensor will typically control a number of lighting fixtures in a space, some areas may be too dark while others are overlighted because daylight rarely penetrates uniformly into a building's interior. Also, daylight penetration may vary at adjacent workstations because workers operate blinds or there are exterior window obstructions.
Significant effort has been directed to solving these problems as evidenced by patents and other references directed to proposed solutions. A summary of some of the more pertinent references follows.
U.S. Pat. No. 4,023,035 issued to Rodriguez discloses a light-sensitive lamp adapter which is small enough to fit in an indoor or outdoor lamp between the lamp socket and a light bulb. The light-sensitive electronic circuitry is entirely contained within the adapter. An adjustable window on the side of the adapter allows the user to have the adapter respond only to light of a selected intensity and incidence on the adapter. The adapter is also characterized by the small size of its internal electronic circuitry and the mode of mounting that circuitry. A solid state switch arrangement in the form of an integral triac/diac chip assembly is mounted directly to a metallic disk positioned against the base of the adapter. Therefore, the '035 patent addresses retrofit for a light-sensitive lamp adapter. This subject matter differs from the present invention in that it is for incandescent sockets only and does not have a self commissioning feature that will allow proper operation under all conditions (e.g., walking between the table lamp and the window could turn on the lights).
U.S. Pat. No. 4,701,669 issued to Head et al. describes a ratio method for commissioning which has similarities in common with the subject invention. The method requires two photo-sensors, however, and does not utilize Andrew Bierman's self-commissioning device innovation. This reference is directed to a compensated light sensor system for controlling the level of light at a work plane so that the level of light at the work plane is maintained substantially constant as daylight entering the room varies.
U.S. Pat. No. 5,668,446 issued to Baker discloses an energy-saving lighting control system for operating fluorescent light fixtures. Light level is controlled according to the light required for the task being done in the area. Sensors detect occupancy and light level. The system provides time-of-day scheduling minimum and maximum lighting levels. A building is divided into several zones, with several zone controllers controlling and powering one or more fluorescent light fixtures and operating the sensors. The zone controllers also transmit manually operated switch inputs that provide on-off and light level requests directly from occupants in the zone. Each fluorescent fixture within each distinct zone receives control signals from a zone controller associated with each distinct zone. Each control zone could have from one to tens of light fixtures, all responding to the same control signals. A central computer passes sensor information between zones to reduce the number of sensors required in a given building. The zone controllers are slaves of the central control computer in that they do not initiate a transmission onto the power line unless they receive a command from the central computer to do so. The central computer allows the operator to directly control light levels in the zone and set minimum and maximum light levels that are suitable for each control zone.
U.S. Pat. No. 5,701,058 issued to Roth is directed to a method of semi-automatic ambient light sensor calibration in an automatic control system. The method utilizes a light meter and a programmer communicating with the lighting control system. The programmer senses the lighting level at the point of interest via the light meter and interactively adjusts the lighting level through the lighting control system, which controls the power controller for the lighting lamps, usually by a dimmable ballast. By reading the ambient light levels with the outdoor lighting at both minimum and maximum levels and with the electrical lighting at both minimum and maximum levels, the programmer calculates the electronic gain and set point required to provide adequate light to the point of interest at any outdoor light level. The method calculates a set point and a gain which are utilized to maintain a constant lighting level at a lighting point of interest. The method requires a technician to enter information into the programmer and to close and open window shades a number of times. The programmer calculates the values of electronic gain and set point based on eight light measurements (see column 5, lines 21–23).
U.S. Pat. No. 5,977,717 issued to Dean discloses a lighting control system that uses a photo-sensor, a comparative circuit, and a logic switching circuit to sense light intensity levels. The system compares the output from the photo-sensor with a number of preset levels in order to produce a logic output which controls the switching of the logic switching circuit between four states: daylight, dusk, night, and dawn. The system avoids the problem of repeated switching on and off as a result of transient light intensity variations. After the light switches on, it will not switch off again until the light intensity rises above another higher predetermined level. After the light switches off, it will switch on again only if the light intensity falls below a different, lower, predetermined value.
U.S. Pat. No. 6,583,573 issued to Bierman discloses a photo-sensor and control system for dimming lighting fixtures to reduce power consumption. The system decreases the amount of controlled light in response to the presence of both uncontrolled ambient light and controlled electric light, the difference in the ratios of an illumination level at a task location to an illumination level at an operational sensor location for uncontrolled light and controlled light, and a user's lighting preference. The photo-sensor of the disclosed invention may be self-commissioned to compensate for the difference in illumination ratios.
The photo-sensor includes a self-powered photocell unit having a photodiode and a wireless transmitter. This arrangement allows the photocell unit to be easily moved for the commissioning procedure. In addition, all commissioning regimens can be taken using the same photodiode, reducing variability caused by differences in sensitivity to spectral differences between daylight and electric light.
With reference to the figures of the '573 patent, the commissioning procedure is programmed into photo-sensor 100 which, in turn, controls the electrical lighting fixture 10 and, therefore, can measure illumination levels with and without electric light 30, calculating the illumination from electric light 30 by subtraction. A commissioning button 118 is provided for operator input during the commissioning. An operator initiates the programmed commissioning procedure by positioning photocell unit 110 at task location 4 as shown in FIG. 7, and pressing commissioning button 118. Photo-sensor 100 then automatically measures the combined daylight 20 and electric light 30 illumination level at task location 4, turns off the electrical light fixture 10, measures the daylight 20 illumination level at task location 4, turns on the electrical lighting fixture 10, and prompts an operator to move photocell unit 110. The operator positions photocell unit 110 at operational sensor location 2, as shown in FIG. 2, and again presses commissioning button 118. Photo-sensor 100 then automatically measures the combined daylight 20 and electric light 30 illumination level at operational sensor location 2, turns off electrical lighting fixture 10, measures a daylight 20 illumination level at operational sensor location 2, turns on electrical lighting fixture 10, and calculates set-point and ratios for use by an illumination control algorithm to compensate for differences in task-to-sensor illumination ratios between daylight and electric light.
A publication entitled “Photoelectric control of equi-illumination lighting systems” by F. Rubinstein, published in Energy and Buildings, 6, pp. 141–150 (1984) discloses a photo-electrically controlled lighting system to maintain a constant light level on a task surface by responding to changing daylight levels. The system is affected by the control algorithm used to relate the photo-sensor signal to electric light levels and by the geometry and location of the photo-sensor. The article discloses equations for a control processor signal that separate the signal into electric light and daylight components. The system consists of three basic components: (1) a control photo-sensor that generates an electrical signal proportional to the amount of light impinging on its surface; (2) a logic circuit that incorporates a control algorithm to process the photo-sensor's signal and convert it to a control signal for a dimming unit; and (3) a dimming unit that smoothly varies the electric light output by altering the amount of power flowing to the lamps. The system can be applied to high-frequency ballasted systems capable of controlling individual fixtures.
The article states, “the algorithm employed by the control system is of crucial importance . . . [T]he simpler the form of the algorithm, the simpler it is to design and operate the system.” See page 143. The simplest control algorithm is a constant set-point algorithm. Once the daylight component of light sensed by the photo-sensor exceeds the maximum defined by the equations, the control system turns off the electric lighting. See page 144.
U.S. Pat. No. 5,357,170 issued to Luchaco et al. discloses a light control system with a priority override. The system is selectively operable in either a normal mode or an off-normal mode. In the normal mode, certain lighting parameters (e.g., maximum and minimum light levels and fade rates) are preset and lighting level is determined by which of a plurality of inputs requires the least electrical power. In the off-normal mode (e.g., a calibration or light-adjustment mode), certain parameters are adjustable by manually adjusting the position of a wiper blade in a potentiometer. A microprocessor-based logic and control unit is adapted to automatically switch from the normal operating mode to the off-normal mode in response to movement of the wiper blade. After a predetermined time period following the most recent movement of the wiper blade, the logic and control unit stores the new level of the adjusted parameter and returns to the normal operating mode.
U.S. Pat. No. 5,498,931 issued to Bedocs discloses automatic switching and control of lighting in a localized area. The switching of the lighting is dependent on the presence or absence of a person in the localized area. The control of the lighting intensity is dependent on the sensed background level of lighting in the localized area. A photocell detects the light level in the operation range. Control electronics receive a signal from the photocell indicating the level of light that is being detected. If the photocell receives a level of light above the turn-off level, the electronics delays a predetermined amount of time before decreasing the lamp output. After that, the control electronics provides an appropriate signal to the inverter and ballast to extinguish the lamps. This stabilizes the system response by preventing the lamps from turning on and off in a rapid and annoying fashion. The control electronics adjust the lamp output to maintain the light level as constant as practicable at a target light level. The control scheme varies the lamp output between a minimum and maximum level as dictated by the ambient light provided by sources other than the lamps under control. The range of lamp output, as well as the target light level, can be selected according to the expected ambient light fluctuations in the environment where the device is installed and according to the intended use of the environment and its lighting requirements.
U.S. Pat. No. 5,894,175 issued to Berlin et al. is directed to a photo-control apparatus and circuit which uses light to regulate the operation of a load. The photo-control circuit includes two or more photocells connected in parallel that respond to ambient light and a switch that uses a bimetal element to connect the power switch to the load. When the photocells are exposed to ambient light, the resistance of the photocells decreases which results in increased current flow causing a heating resistor to dissipate additional heat. The additional heat forces the bimetal element to expand which thereby disengages the load from the source. In the absence of light, the resistance of the photocells increases, limiting the heat and allowing the switch to remain in a closed position. This couples the load to the source. FIG. 3 illustrates a prior art version of a photo-control apparatus which embodies a single photocell.
U.S. Pat. No. 6,294,874 issued to Rudolph et al. is directed to a ceiling fan assembly that includes a light-sensitive circuit for controlling an illumination level of a light as a function of an ambient illumination level surrounding the ceiling fan assembly by selectively controlling or fixing a conduction phase angle of an AC power signal provided to the light. The light-sensitive circuit includes a photocell that is responsive to the ambient illumination level. The light-sensitive circuit operates as a function of ambient illumination surrounding the ceiling fan assembly. The light-sensitive circuit illuminates at selective percentages of a fully-on illumination level as a function of an ambient light level; illuminates at a fully-on illumination level or a fully-off illumination level regardless of the ambient light level; and avoids flicker from the light operating at low levels of illumination.
A paper entitled “Characterizing daylight photosensor system performance to help overcome market barriers” by A. Bierman et al, published in the Journal of Illuminating Engineering Society (Winter 2000) discloses theoretical underpinnings for a daylight photo-sensor system that could control illumination efficiently by balancing the use of daylight and electric light and would offer occupants a satisfactorily illuminated working environment in office buildings. The article discloses that “[t]he control algorithm is the most important functional element of the photo-sensor system,” see page 108, and that it “dominates the performance of the photo-sensor system,” see page 110. According to the article, the main division of separate functions is between the optical and electrical characteristics. The optical functions serve two main purposes: (1) they collect ambient radiation and direct it onto the photocell, where it is converted into an electrical signal; and (2) they make the response of the photo-sensor wavelength selective in some way so that it can be related to photometric quantities. The electrical function modifies the photocell signal to produce the desired control-algorithm response. The control algorithm can be further divided into a steady-state response and a temporal response. The link between the optical response functions and the control algorithm can be made by reporting the control algorithm as a function of photo-sensor illuminance for a specific wavelength and incident direction.
U.S. Pat. No. 4,461,977 issued to Pierpoint et al. discloses a zone lighting controller that controls lights by integrating external control signals for daylight and occupancy with a local override function. The daylight signal is from a master photoelectric control and the occupancy signal is from a time clock or electronic occupancy sensor. The lighting controller turns the lights off if there is either sufficient daylight or if the zone is vacant and turns the lights on if there is insufficient daylight and the room is occupied. The override switch allows the light to be on for a preset period of time regardless of the control signals from the daylight and occupancy sensors.
A paper entitled “A comparison of photosensor-controlled electronic dimming systems in a small office” by R. Mistrick et al., published in the Journal of the Illuminating Engineering Society (Winter 2000) analyzed six commercially available photo-sensors and their associated control algorithms. Although the study addressed the ability of the sensors to be optimally fit to a series of daylight conditions, it did not address the ability of the sensors to be appropriately calibrated under real room conditions. The article notes that “[c]alibration presents a potential problem since the actual performance of a control system is based on a setting that is derived at a single daylight condition. If this condition is not carefully selected, the resulting performance may be different than desired.” See page 71.
U.S. Pat. No. 4,021,679 issued to Bolle et al. discloses a method and apparatus for automatically switching artificial light. The light is turned on by a person entering the area and reflecting an ultrasonic wave pattern toward a receiver. The light is turned off by a person moving into contactless proximity of a capacitance comparison circuit which uses the capacitance of the human body as one of the circuit elements. The system uses a photocell to operate at different levels of sensitivity, depending upon the existing available light in the area.
U.S. Pat. No. 4,523,132 issued to Christiansen et al. relates to a lighting system having a plurality of individual light points that can be controlled by a central switch element. The central switch element includes a light sensor and a dimness switch. Manually operated switches may be used to override the central switch.
U.S. Pat. No. 6,003,160 issued to Seidle et al. discloses an automatic self-illuminating toilet lid. The toilet lid has a light source that can automatically be switched on and off using a gravity switch when the toilet lid is raised and lowered. A light sensor opens a circuit when room light or daylight is detected, thus preventing batteries from lighting the lamp.
U.S. Pat. No. 6,422,714 issued to Hubbell discloses an illuminated outdoor sign with two photo-sensors that control when the sign is illuminated. One photo-sensor responds to ambient light level. It is shielded from artificial light such as street lights and lights from vehicles. The second photo-sensor responds to a vehicle's headlights. It is shielded from ambient light and other sources of artificial light. When both photo-sensors are on, a lamp in the sign is illuminated.
To overcome the shortcomings of prior art photosensor systems, a new photosensor switch is provided. An object of the present invention is to provide improved building end-use efficiency. A related object is to significantly reduce the lighting energy used in commercial buildings with significant daylight contribution either through windows or skylights. Another object is to reduce peak load requirement.
It is still another object of the present invention to have a system that is easy to install, requiring no additional runs of wire. An additional object is to use the system with existing wiring within a lighting fixture. Yet another object of this invention is to use the invention with conventional ballast technologies, including instant start ballasts, without the need to replace ballast. A further object of the invention is have a system that is self-commissioning and will not require a lighting specialist. It is yet a further object of the invention that the system will individually control only one lighting fixture, which will be turned off only if sufficient daylight is available in the area where that particular fixture is installed. It is yet a further object of the invention to alleviate the problem of having uneven light distribution within a space.